Antennas comprising coaxial waveguides having slotted outer conductors have been widely used to transmit television signals. In recent years it has become increasingly popular to transmit television signals with circular polarization, primarily to improve the reception of such signals in congested metropolitan areas. As is well known, a transmitting antenna can produce a circularly polarized wave by radiating separate vertically and horizontally polarized waves having the same amplitude with a 90.degree. phase difference. Any departure from the equal amplitudes and/or the 90.degree. phase difference produces an elliptically polarized wave, with the degree of ellipticity expressed as the "axial ratio", which is the ratio of the major axis to the minor axis of the ellipse.